Free fraction measurement

The position of equilibrium lies strongly to the left. However, it is the free form of the hormone which is physiologically active with the bound fraction acting as reserve supply . Typically therefore, the plasma total concentration of the hormone (bound + free fractions, measured typically in nmol/1) is of the order of 1000 times higher than the concentration of the free fraction alone (measured typically in pmol/1 concentrations). 

Recoil-free fraction measurements for soUd krypton between 5 K and 85 K are also available [19,20], but in this case the / values are lower than expected. Some of the first calculations [20] omitted the effects of anharmonicity upon the phonon frequency spectrum. Inclusion of an harmonic effect [21] gives better agreement between experiment and theory, but the zero-temperature limit of / is anomalously low and has still not been explained. 

This ratio is one if /(0) is isotropic. If /(0) has the form given by Equation (6.7), this ratio will depend only on the value of fe xf>-relative intensities in an absorption spectrum gives the value of this parameter directly. If in addition the total absorption intensity is measured, the average recoil-free fraction can be estimated. If aj and bf are the nuclear transition probabilities for the Am, = 0 and Aw, = + l transitions respectively, then the average recoil-free fraction, measured... 

The example is typical for many applications of Mossbauer spectroscopy in catalysis a catalyst undergoes a certain treatment, then its Mossbauer spectrum is measured in situ at room temperature. Flowever, if the catalyst contains highly dispersed particles, the measurement of spectra at cryogenic temperatures becomes advantageous as the recoil-free fraction of surface atoms increases substantially at temperatures below 300 K. Secondly, spectra of small particles that behave superparamagne-... 

However, in contrast, the resonance effect increased by cooling both the source and the absorber. Mdssbauer not only observed this striking experimental effect that was not consistent with the prediction, but also presented an explanation that is based on zero-phonon processes associated with emission and absorption of y-rays in solids. Such events occur with a certain probability/, the recoil-free fraction of the nuclear transition (Sect. 2.4). Thus, the factor/is a measure of the recoilless nuclear absorption of y-radiation - the Mdssbauer effect. 

The recoil-free fraction /a of transition metal complexes or proteins in frozen solution can be as small as 0.1-0.3, when measured just below the melting point, but the /-factor increases strongly when the temperature is lowered to fiquid nitrogen temperatures (77 K), and at fiquid helium temperatures (4.2 K) it may reach values of 0.7-0.9 [35]. This makes a substantial difference to the acquisition time of the spectra because of the square dependency on the signal (3.1). 

The high atomic mass yields small recoil energies and thus a large recoU-free fraction even at room temperature (/300 0.95 for Ta metal [175]) this allows measurements of the resonance effect to be made over a wide temperature range up to about 2,300 K. 

Kaltseis et al. [234] have investigated the recoil-free fraction of the 46.5 keV transition of W in anhydrous lithium tungstate. Their results can be expressed by an effective Debye temperature of 172 9 K which is in good agreement with a value of 205 40 K derived from X-ray diffraction measurements of Li2W04 powder. 

Wender and Hershkowitz [237] used the sensitivity of the recoil-free fraction in tungsten Mossbauer spectroscopy to deduce the effect of irradiation of tungsten compounds by Coulomb excitation of the resonance levels (2 states of I82,i84,i8 y with 6 MeV a-particles. While no effect of irradiation on the/-factors could be observed for tungsten metal in agreement with [233], a decrease of/was measured for WC, W2B, W2B5, and WO3 after irradiation. 

The paper summerizes the experimental data on the equilibrium factor, F, the free fraction, fp, the attachment rate to the room air aerosol, X, the recoil factor,, and the plateout rates of the free, qf, and the attached, q3, radon daughters, determined in eight rooms of different houses. In each room several measurements were carried out at different times, with different aerosol sources (cigarette smoke, stove heating etc.) and under low (v<0.3 It1) and moderate (0.3[Pg.288]

For the determination of the free fraction the attached and the total radon daughter activity concentration were measured. The separation of the free radon daughters from the total daughter concentration was carried out by means of a high-volume diffusion screen battery (Reineking and Porstendorfer, 1986) with a 50 % penetration efficiency for 4 nm particles and for a flowrate of 2.4 m h-1. ... 

All our measurements i/ere carried out in rooms with i < 1 hr1 and the radon concentration outdoors (c 5 Bq nr 3) i/as always much smaller than indoors (cj > 100 Bq m 3). Assuming a constant radon emanation, a homogeneous activity distribution and 100 % prefiltering of the free fractions of the incoming air, the radon, the free and attached radon daughter activity concentrations indoors (cj cjf cja) and outdoors (eg c f c a) under steady conditions are ... 

The concentrations of radon (cj) and the free (c f, c2f ) and on aerosol attached (cja, cja, cja radon daughters vi/ere measured and with these data the equilibrium factor F and the free fraction of the radon daughters fp were calculated. The room parameters (e, v) and the parameters of radon daughter transport processes (X, qf, q3, ri) were evaluated by means of equations (3), (4), (8), (9), (10) and (11) using the measured data. 

The free fraction of the radon daughters f measured in rooms with lo i/ ventilation and no aerosol sources shows values between 0.06 - 0.15 (Table lb) with a mean value near 0.10. In this case the values of the attachment rates X range between 20 hr and 40 hr. The fp-values < 0.05 were obtained in rooms with aerosol sources, which always had values of the attachment rate > 100 It1 (Table III). 

Table lb. The equilibrium factor (F), the free fraction (fp), the attachment parameters (X,0,d), the plateout rates (qf, qa) and the recoil factor (r ), calculated from the measured data of Table la (lo i/ ventilation). 

Measurement of the ratio of radioactivity in the bound and free fractions. 

In a radioimmunoassay procedure, 1 pmol of labelled analyte was added to the sample. Antiserum equivalent to 75 pmol of analyte was then added, and after incubation the bound and free fractions separated by precipitation with ammonium sulphate solution. The activity ratio, bound free, was measured to be 2.88. Calculate the number of moles of analyte in the original sample. 

Figure 5.2 The recoil-free fraction,/, of iron as a function of temperature for different values of the Debye temperature, 6 y Bulk iron compounds have Debye temperatures on the order of 450-500 K surface phases, however, have significantly lower Debye temperatures, implying that measurements may have to be carried out at lower temperatures...

Thus making samples not too thick helps in getting sharper spectra and facilitates the quantitative interpretation. Finally, particularly in the Mossbauer spectra of small catalyst particles, one should be aware of the temperature dependence of the absorption area through the recoil-free fraction. If the spectrum contains contributions from surface and bulk phases, the intensity of the former will be greatly underestimated if the spectrum is measured at room temperature. The only way to obtain reliable concentrations of surface and bulk phases is to determine their spectral contributions as a function of temperature and make an extrapolation to zero Kelvin [13]. 

Surface phases have low Debye temperatures. As a result, the recoil-free fraction may be low at room temperature (see Fig. 5.2). Thus, measuring at cryogenic temperatures will increase the Mossbauer intensity of such samples considerably. But there can also be other circumstances which call for low temperature experiments. 

A recent report on a NR2B selective NMDA receptor antagonist (9) supports the findings of Kalvass and Maurer [56], Rapid equilibration between plasma and CNS coupled with the lack of Pgp substrate activity led the authors to assume that plasma-free and brain-free drug concentrations were equivalent. An ex vivo receptor binding assay showed 50% occupancy at a total plasma concentration of 230 nM. Given a rat-free fraction of 15.3%, the authors concluded that 50% brain occupancy occurred at 35 nM unbound brain concentration, which was in reasonable agreement with the measured Ki of 3.4 nM versus the human receptor. 

The viscosity dependence of intramolecular excimer formation is complex. As in the case of molecular rotors (Section 8.2), most of the experimental observations can be interpreted in terms of free volume. However, compared to molecular rotors, the free volume fraction measured by intramolecular excimers is smaller. The volume swept out during the conformational change required for excimer formation is in fact larger, and consequently these probes do not respond in frozen media or polymers below the glass transition temperature. 

In a series of papers, Diphant has been used to probe the microviscous properties of various polymer oils, and free volume parameters have been extracted. 4,88 90) In a comparative study of Excimer and TICT probes, it could be shown that the response of these probes is frozen out at lower temperatures, as can be expected from the large reaction volume necessary, whereas the TICT reaction still shows sizable rates at these high-viscosity conditions. (26) Moreover, this study also showed that the free volume fraction measured by the TICT probes is larger than that measured by Excimer probes. 

Nonisotopic Immunoassays. Nonisotopic immunoassays differ from the isotopic assays only in the type of label used, the end-point measurement, and the separation of bound and free fractions (41-43). 

UFF and UFE [62]. 18-OHF is also better analyzed in the free fraction, since we find that the enzyme hydrolysis has a deleterious effect on the steroid. Derivatization is carried out after Sep-Pak extraction of 5 ml of urine without hydrolysis. Two or four peaks were given for each steroid on account of syn- and anti- forms of the oxime derivative all were integrated. Dideutero internal standards are not ideal as there is significant contribution of analyte to the internal standard, and vice-versa. It is therefore important to utilize standard curves or a correction formula based on the measured contributions. Results obtained for normal males and females using this methodology are given in Table 5.3.2. 

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